The present invention relates to navigation systems and more particularly the present invention relates to providing guidance when a driver deviates from a route for which route guidance was previously being provided a navigation system.
Navigation systems provide useful features, such as calculating a route to a desired destination and providing guidance for following the route. In order to provide these features, navigation systems use geographic data that include information about the locations of roads and intersections, estimated travel times along road segments, the speed limits along roads, etc. Using these kinds of geographic data, programming algorithms included in navigation systems can find an optimal (e.g, fastest or shortest) route to a specified destination.
Some navigation systems provide a feature that can detect if a vehicle has departed from a route for which route guidance was being provided (i.e., when the vehicle has gone "off-route"). Upon detecting that the vehicle has gone off-route, the navigation system calculates a new route to either the destination or back to the original route and provides guidance to the vehicle driver for following the new route. A factor that can complicate providing this feature is that the calculation of the new route may take several seconds during which time the vehicle position may change. Therefore, the point of origin from which the new route was calculated may not be valid several seconds later when the guidance for following the new route is available for the driver. Worse still, the vehicle driver may have encountered an intersection before the route guidance for following the new route was available and chosen a path leading from the intersection that was not part of the new route. If this occurs, the vehicle is off-route of the new route when the new route becomes available thereby necessitating calculation of another new route from the vehicle position to either the destination or back to the original route.
Accordingly, there exists a need in a navigation system to provide route guidance to a user when the vehicle in the navigation system goes off-route.